Temperature measurement

ABSTRACT

The temperature of molten steel in a converter is measured by blasting an inert gas through a tube into the melt so as to provide a gas/liquid interface adjacent the end of the tube and measuring the temperature of the melt by sighting radiation pyrometer along the tube through the gas towards the interface. More particularly the gas is heated e.g. by a plasma arc, to a temperature approximating that of the melt. The tube may depend into the converter from above or it may extend through the wall of the vessel below the surface of the melt.

United States Patent 1 Stanworth et al.

[ July 24, 1973 TEMPERATURE MEASUREMENT [75] Inventors: Colin GrahamStanworth, Penbryn; John Dixon; David Ian Jones, both of Rotherham, allof England [73] Assignee: British Steel Corporation, London,

England 22 Filed: Oct. 13, 1971 21 App1.No.: 188,839

[30] Foreign Application Priority Data Oct. 15, 1970 Great Britain49,097/70 [52] U.S. Cl 73/355 EM, 73/355 R, 356/44, 356/45 [51] Int. ClG0lj 5/04, G01] 5/60 [58] Field of Search 73/355 R, 355 EM, 73/351;356/43-45 [56] References Cited UNITED STATES PATENTS 12/1942 Percy73/355 R X 2,815,276 12/1957 Michaux 2,395,937 3/1946 Paalu 731355 R UXFOREIGN PATENTS OR APPLICATIONS 1,004,123 3/1952 France 73/355 R OTHERPUBLICATIONS Translation of French Patent 1,004,123. Method andApparatus for Temperature Determination of Pneumatic Converter Bath.

Primary Examiner-Richard C. Queisser Assistant ExaminerFrederick ShoonAtt0rney-Bacon & Thomas [57] ABSTRACT The temperature of molten steel ina converter is measured by blasting an inert gas through a tube into themelt so as to provide a gas/liquid interface adjacent the end of thetube and measuring the temperature of the melt by sighting radiationpyrometer along the tube through the gas towards the interface.

More particularly the gas is heated e.g. by a plasma are, to atemperature approximating that of the melt. The tube may depend into theconverter from above or it may extend through the wall of the vesselbelow the surface of the melt.

7 Claims, 4 Drawing Figures PATENTED JUL24|375 3, 747, 408

SHEET 1 0F 3 PATENTEDJUL24I973 p I I I I 4 r r I I A! r I r I I I I I II1 r z a 4 SHEET 2 BF 3 llllll lllllllllllllllllllllllllll IL TEMPERATUREMEASUREMENT This invention relates to temperature measurement, and moreparticularly relates to measurement of the temperature of a liquid, e.g.molten iron or steel.

An important parameter in the control of steelmaking processes is thetemperature and there are a number of methods of measurement which canbe employed involving, for example, (a) immersion thermocouples (b) wallthermocouples and (c) radiation pyrometers. The first of these methodsrequires the steelmaking process to be suspended whilst measurements aremade and the second tends not to give the true temperature of the melt.

Radiation pyrometers, the other alternative, have hitherto suffered fromdifficulties in obtaining a clear sight path through fume and flame andin conventional use there is a possibility of them reading thetemperature, not of the molten steel, but a cooler slag coating;otherwise however, they are accurate and convenient to use.

It is an object of this invention to provide an improved method of, andapparatus for, measuring the temperature of a liquid utilising thisinstrument.

From one aspect the invention provides a method of measuring thetemperature of a liquid, in which a gas is blasted through a tube intothe liquid to provide a gas/liquid interface adjacent the end of thetube and in which the liquid temperature is measured by a radiationpyrometer sighted along this tube through the gas towards the interface.

Similarly, the invention also provides apparatus for measuring thetemperature of a liquid, comprising a tube for contacting the liquid atone end, means for blasting a gas through the tube into the liquid so asto provide a gas/liquid interface adjacent the said end, and a radiationpyrometer for measuring the liquid temperature sighted along the tubethrough the gas towards the interface.

The liquid may be molten metal and in this instance the gas ispreferably inert to the melt so as to avoid the establishment of areaction zone at the end of the tube which would give rise to falsetemperature readings, and so as not to affect the composition of themelt. The gas may also be preheated to a temperature similar to that ofthe melt, and this is particularly advantageous compared with a cold"gas purge since heat is supplied to the melt, inhibiting the tendencyfor the metal' to solidify around the end of the tube; in addition, theresultant thermal expansion of the gas reduces the amount of this mediarequired for the operation.

The tube may be immersed into the melt from above, e.g. through themouth of a convcrtor in a steelmaking process, or it may be built intothe base of the vessel so that it is covered by the contents. Thepyrometer is preferably mounted in this tube and sighted through asilica window, and the pyrometer employed may be of the two-colour typesince it is substantially independent of both the emissivity of thetarget" and atmospheres containing a moderate amount of flame and fume,and is insensitive to partial obscuration of the target area.

In order that the invention may be fully understood two embodimentsthereof will now be described, by way of example, with reference to theaccompanying drawings in which:

FIG. 1 schematically illustrates a cross-sectional view through aBessemer convcrtor in which the temperature-measuring apparatus issituated in the base;

FIG. 2 illustrates one form of this apparatus;

FIG. 3 illustrates a cross-section through A-A in FIG. 2; and

FIG. 4 illustrates another form of this apparatus.

Referring now to FIG. 1, a Bessemer convcrtor is illustrated having arefractory-lined casing l and a tuyere plug 2 through which extendtuyeres 3. A wind box 4 through which air is blasted into the molteniron charge is mounted below the plug, and a sight tube 5 with which thetemperature measuring apparatus is aligned extends through this plug.This tube extends as near vertically through the plug as practicable sothat there is negligible difference in the ferrostatic head across theinner orifice of the tube. If this were not the casethere may be atendency for the iron to run into the tube and freeze along the walls.

In FIGS. 2 and 3, one form of the temperature measuring apparatus isillustrated in which it is located within the sight tube 5 itself. Inthis instance, two tubular members 6, 7 are provided, one housing atwocolour radiation pyrometer 8 and the other housing a plasma gun 9.Both of these items are water-cooled, the water running along a path 10up one side of these members through a bridging duct 11 and down theother side 12.

The pyrometer, which determines temperature from the ratio ofintensities emitted at two discrete wavelengths, includes a silicasealing window 13 adjacent to which is a lens 14 for focusing theincident energy on to a detector head, the output being taken through alead 15 at the base of this instrument.

The plasma gun comprises an anode l6 watercooled through ducts 17extending between the paths 10, 12 and an elongated cathode 18.

A gas inlet circuit 19 is provided adjacent the cathode l8 and arefractory lining 20 extends around the inside of the tubular member 7upstream" of the anode.

In operation, gas, e.g. argon, is blasted through the conduit 19 intothe plasma gun, the gun is ignited and the gas is heated to a very hightemperature (e.g. l,000 C) as it traverses the arc drawn between theanode and cathode. The incoming gas cools the cathode whilst the hightemperature gas issuing from the gun is forced upwardly through thesight tube into the molten metal in the convcrtor.

The pressure of the gas, which may be about 30 lbs per square inch, issuch as to purge the passage and provide a continuous series of bubblesat the mouth of the sight tube which successively break away from theend, the line of sight for the pyrometer thus being cleared so that thetemperature of the melt at the gas/- liquid interface is measureddirectly by the pyrometer through this gaseous medium.

As mentioned, the apparatus shown in FIGS. 2 and 3 is mounted within thesight tube, but in FIG. 4 an alternative scheme is shown in which atwo-colour radiation pyrometer is utilised having a smaller angle ofacceptance" for the radiation, thus allowing it to be situated outsidethe vessel. This mode of construction also enables the plasma gun andthe pyrometer to be separately detachable, facilitating replacement andservic- In particular, a refractory sleeve 21 is clamped to the sighttube 5 and the pyrometer 8 is directly aligned with this tube through apair of silica windows 22 spaced apart by a copper sleeve 23. Thepyrometer is mounted in a water-cooled jacket 24, the pyrometer/jacketas- I sembly being readily detachable from the sleeve 21.

The plasma gun 9 is teed into the refractory sleeve and, as before,comprises a cathode and a water-cooled anode, separate conduits 25 nowbeing provided for the latter. A gas inlet conduit 26 is provided on thegun adjacent the cathode and, in operation, gas is blasted through thisconduit into the gun and upwardly through the sight tube into the moltenmetal in the convertor.

Although the invention has been described with reference to theparticular embodiment illustrated it is to be understood that variousmodifications and alterations may readily be adopted without departingfrom the scope of this invention. For example, various safety schemesmay be incorporated to ensure that the plasma arc is not initiatedbefore the purge gas flows, and that the sight tube will be purged withan enhanced gas flow should the plasma gun fail to ignite so as to keepthe tube clear and prevent the metal freezing and scabbing around it. Anauxiliary supply of gas may also be coupled in circuit for emergencypurposes.

Provision may also be made to automate the temperature measurementenabling the gas purge to start whenever the blast is switched on to thevessel, and the plasma gun to be ignited. Subsequently, after the blasthas been removed and the convertor tilted and discharged, the purge gasis maintained for a short while so that any liquid slag remaining afterthe heat drains away from the sight hole into the vessel.

Further, although the invention has been described in connection withsteelmaking in a Bessemer convertor, it is to be understood that it isequally applicable to other vessels, for example, an LD convertor, and,as mentioned above, the apparatus need not be sited in the base of thevessel it could readily be lowered through the mouth in a lance. Inaddition, although reference has been made to the use of argon gas othergases may alternatively be employed, for example, blast furnace gas,which is in plentiful supply, or nitrogen if this is acceptable.

We claim:

1. Apparatus for measuring the temperature of a molten metal in avessel, comprising a tube having one end which contacts the melt,

an inert gas source,

heater means for preheating the gas to a temperature approximating thatof the melt,

pressure means for blasting the gas through the tube into the melt so asto create a gas/liquid interface adjacent the said one end of the tube,and

a radiation pyrometer for measuring the temperature of the melt sightedalong the tube through the gas towards the interface.

2. Apparatus according to claim 1, wherein the heater means comprises aplasma arc gun.

3. Apparatus according to claim 2, wherein the tube includes twochannels, one of said channels containing the pyrometer and lying inalignment with the gas/liquid interface and the other channelcommunicating with the said one channel and containing the plasma arcgun.

4. Apparatus according to claim 1, wherein the radiation pyrometer is ofthe two-colour type.

5. Apparatus according to claim 4, wherein the tube projects through thevessel at a level below the surface of the melt.

6. Apparatus according to claim 4, wherein the tube is immersed into thesurface of the melt.

7. A method of measuring the temperature of a mol ten charge in a vesselcomprising:

preheating a gas inert to the melt to a temperature approximating thatof the melt, blasting said gas through a tube into the melt to provide agas/liquid interface adjacent the end of the tube, and

measuring the temperature of the melt by a radiation pyrometer sightedalong the tube through the gas towards the interface.

1. Apparatus for measuring the temperature of a molten metal in avessel, comprising a tube having one end which contacts the melt, aninert gas source, heater means for preheating the gas to a temperatureapproximating that of the melt, pressure means for blasting the gasthrough the tube into the melt so as to create a gas/liquid interfaceadjacent the said one end of the tube, and a radiation pyrometer formeasuring the temperature of the melt sighted along the tube through thegas towards the interface.
 2. Apparatus according to claim 1, whereinthe heater means comprises a plasma arc gun.
 3. Apparatus according toclaim 2, wherein the tube includes two channels, one of said channelscontaining the pyrometer and lying in alignment with the gas/liquidinterface and the other channel communicating with the said one channeland containing the plasma arc gun.
 4. Apparatus according to claim 1,wherein the radiation pyrometer is of the two-colour type.
 5. Apparatusaccording to claim 4, wherein the tube projects through the vessel at alevel below the surface of the melt.
 6. Apparatus according to claim 4,wherein the tube is immersed into the surface of the melt.
 7. A methodof measuring the temperature of a molten charge in a vessel comprising:preheating a gas inert to the melt to a temperature approximating thatof the melt, blasting said gas through a tube into the melt to provide agas/liquid interface adjacent the end of the tube, and measuring thetemperature of the melt by a radiation pyrometer sighted along the tubethrough the gas towards the interface.